The aim of this project is to examine gastric epithelial cells, their ability to secrete mucus in response to parasympathetic stimuli, and specifically to determine whether secretion is due to exocytosis, a process dependent on the microtubular cytoskeleton. Canine gastric mucosa will be studied in the in vitro Ussing Chamber model in order to eliminate humoral, blood flow and "mechanical"-contractile effects on mucus secretion. Glycoproteins will be radiolabeled with either free 35SO4 or 3H glucosamine, and secretion of sulfate and total glycoprotein measured by the appearance of label in the gastric secretion. The effects on mucus secretion of cholinergic, adrenergic and serotonergic neurohormones alone, and in combination with their respective antagonists will be tested in a dose response manner. Autoradiography and light microscopy of harvested mucosae will be used to determine if neural stimuli selectively stimulate pit epithelial cells or all cells of the gastric epithelium; the former implying that deeper mucus cells are neurally innervated. The ultrastructural correlates of secretion will be determined by transmission and scanning electron microscopy. If exocytosis is shown to be the primary mode of stimulated release, an attempt will be made to inhibit sustained secretion by disrupting microtubules with colchicine. Microtubules have been shown to be intimately involved in the exocytic secretory process because they convey mucus granules to the apical surface. The effect of colchicine on the intracellular movement of mucus granules from the Golgi through the apical mucus package will be examined autoradiographically. If apical expulsion is the mechanism of stimulated secretion, microtubular inhibitors will likely have no effect because the process is an invaginating one in which granules coalesce and mucus flow outward. The outlined project is an attempt to better understand basic cell function, namely gastric mucus secretion.